LC2MOS
Microprocessor-Compatible 14-Bit DAC
AD7538
FEATURES
FUNCTIONAL BLOCK DIAGRAM
VDD
All grades 14-bit monotonic over the full temperature range
Low cost, 14-bit upgrade for 12-bit systems
14-bit parallel load with double buffered inputs
Small 24-pin, 0.30” DIP and SOIC
Low output leakage (<20 nA) over the full temperature range
VREF 1
APPLICATIONS
Microprocessor-based control systems
Digital audio
Precision servo control
Control and measurement in high temperature environments
2
RFB
14-BIT DAC
3
IOUT
4
AGND
DAC REGISTER
20
LDAC
INPUT
REGISTER
21
CS
22
WR
14
6
5
24
DGND
VSS
19
DB13 TO DB0
01139-001
23
AD7538
Figure 1.
GENERAL DESCRIPTION
PRODUCT HIGHLIGHTS
The AD7538 is a 14-bit monolithic CMOS digital-to-analog
converter (DAC) that uses laser trimmed thin-film resistors to
achieve excellent linearity.
1.
The DAC is loaded by a single 14-bit wide word using standard
chip select and memory write logic. Double buffering, which is
optional using LDAC, allows simultaneous updates in a system
containing multiple AD7538s.
2.
3.
A novel low leakage configuration enables the AD7538 to
exhibit excellent output leakage current characteristics over
the specified temperature range.
4.
The AD7538 is manufactured using the linear-compatible
CMOS (LC2MOS) process. It is speed compatible with most
microprocessors and accepts TTL or CMOS logic level inputs.
5.
Guaranteed Monotonicity.
The AD7538 is guaranteed monotonic to 14-bits over the
full temperature range for all grades.
Low Cost.
The AD7538, with its 14-bit dynamic range, affords a low
cost solution for 12-bit system upgrades.
Small Package Size.
The AD7538 is packaged in a small 24-pin, 0.3" DIP and a
24-pin SOIC.
Low Output Leakage.
By tying VSS (Pin 24) to a negative voltage, it is possible to
achieve a low output leakage current at high temperatures.
Wide Power Supply Tolerance.
The device operates on a +12 V to +15 V VDD, with a ±5%
tolerance on this nominal figure. All specifications are
guaranteed over this range.
Rev. B
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarks and registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2009 Analog Devices, Inc. All rights reserved.
AD7538
TABLE OF CONTENTS
Features .............................................................................................. 1
Equivalent Circuit Analysis ...................................................... 10
Applications ....................................................................................... 1
Digital Section ............................................................................ 10
Functional Block Diagram .............................................................. 1
Unipolar Binary Operation (2-Quadrant Multiplication) .... 10
General Description ......................................................................... 1
Bipolar Operation (4-Quadrant Multiplication) .................... 11
Product Highlights ........................................................................... 1
Low Leakage Configuration...................................................... 11
Revision History ............................................................................... 2
Programmable Gain Amplifier ................................................. 12
Specifications..................................................................................... 3
Application Hints ........................................................................... 13
AC Performance Characteristics ................................................ 4
Output Offset .............................................................................. 13
Timing Characteristics ................................................................ 4
General Ground Management.................................................. 13
Timing Diagram ........................................................................... 5
Microprocessor Interfacing ....................................................... 13
Absolute Maximum Ratings............................................................ 6
AD7538-to-8086 Interface ........................................................ 13
ESD Caution .................................................................................. 6
AD7538-to-MC68000 Interface ............................................... 13
Pin Configuration and Function Descriptions ............................. 7
Digital Feedthrough ................................................................... 14
Terminology ...................................................................................... 8
Outline Dimensions ....................................................................... 15
DAC Section ...................................................................................... 9
Ordering Guide .......................................................................... 16
Circuit Information ........................................................................ 10
REVISION HISTORY
1/09—Rev. A to Rev. B
Updated Format .................................................................. Universal
Changes to Table 1 ............................................................................ 3
Updated Outline Dimensions ....................................................... 15
Changes to Ordering Guide .......................................................... 15
5/87—Rev. 0 to Rev. A
Rev. B | Page 2 of 16
AD7538
SPECIFICATIONS
VDD = 11.4 V to 15.75 V 1 , VREF = 10 V; VPIN3 = VPIN4 = 0 V, VSS = −300 mV; all specifications TMIN to TMAX, unless otherwise noted.
Table 1.
A, J
Versions
B, K
Versions
S Version
T Version
Unit
14
±2
14
±1
14
±2
14
±1
Bits
LSB max
±1
±1
±1
±1
LSB max
±4
±8
±2
±4
±5
±2
±4
±10
±2
±4
±6
±2
LSB max
LSB max
ppm/°C typ
±5
±10
±25
±5
±10
±25
±5
±20
±150
±5
±20
±150
nA max
nA max
nA max
All digital inputs 0 V
VSS = –300 mV
VSS = 0 V
3.5
10
3.5
10
3.5
10
3.5
10
kΩ min
kΩ max
Typical input resistance = 6 kΩ
2.4
0.8
2.4
0.8
2.4
0.8
2.4
0.8
V min
V max
±1
±10
7
±1
±10
7
±1
±10
7
±1
±10
7
μA max
μA max
pF max
VIN = 0 V or VDD
11.4/15.75
11.4/15.75
11.4/15.75
11.4/15.75
V min/V max
VSS Range
−200/−500
−200/−500
−200/−500
−200/−500
IDD
4
500
4
500
4
500
4
500
mV min/
mV max
mA max
μA max
Specification guaranteed over
this range
Specification guaranteed over
this range
All digital inputs are VIL or VIH
All digital inputs are 0 V or VDD
Parameter 2
ACCURACY
Resolution
Relative Accuracy
Differential Nonlinearity
Full-Scale Error
+25°C
TMIN to TMAX
Gain Temperature Coefficient 3 ;
ΔGain/ΔTemperature
Output Leakage Current
IOUT (Pin 3)
25°C
TMIN to TMAX
TMIN to TMAX
REFERENCE INPUT
Input Resistance (Pin 1)
DIGITAL INPUTS
VIH (Input High Voltage)
VIL (Input Low Voltage)
IIN (Input Current)
25°C
TMIN to TMAX
CIN (Input Capacitance)3
POWER SUPPLY
VDD Range
1
Test Conditions/Comments
All grades guaranteed
monotonic
Over temperature
Measured using internal RFB DAC
Registers loaded with all 1s
Specifications are guaranteed for a VDD of 11.4 V to 15.75 V. At VDD = 5 V, the device is fully functional with degraded specifications.
Temperature range as follows: J, K Versions: 0°C to +70°C
A, B Versions: −25°C to +85°C
S, T Versions: −55°C to +125°C
3
Sample tested to ensure compliance.
2
Rev. B | Page 3 of 16
AD7538
AC PERFORMANCE CHARACTERISTICS
These characteristics are included for design guidance only and are not subject to test. VDD = 11.4 V to 15.75 V, VREF = 10 V, VPIN3 = VPIN4 =
0 V, VSS = 0 V or −300 mV, output amplifier is AD711 except where noted.
Table 2.
Parameter
Output Current Settling Time
TA = 25°C
TA = TMIN, TMAX
1.5
Unit
μs max
Digital-to-Analog Glitch Impulse
20
nV-sec typ
Multiplying Feedthrough Error
3
5
mV p-p typ
±0.01
±0.02
% per % max
ΔVDD = ±5%
260
130
260
130
pF max
pF max
DAC register loaded with all 1s
DAC register loaded with all 0s
nV√Hz typ
Measured between RFB and IOUT
Power Supply Rejection
ΔGain/ΔVDD
Output Capacitance
COUT (Pin 3)
COUT (Pin 3)
Output Noise Voltage Density
(10 Hz to 100 kHz)
15
Test Conditions/Comments
To 0.003% of full-scale range
IOUT load= 100 Ω, CEXT = 13 pF DAC register alternately loaded
with all 1s and all 0s; typical value of settling time is 0.8 μs
Measured with VREF = 0 V. IOUT load = 100 Ω, CEXT = 13 pF; DAC
register alternately loaded with all 1s and all 0s
VREF = ±10 V, 10 kHz sine wave DAC
Register loaded with all 0s
TIMING CHARACTERISTICS
VDD = 11.4 V to 15.75 V, VREF = 10 V, VPIN3 = VPIN4 = 0 V, VSS = 0 V or −300 mV. All specifications TMIN to TMAX unless otherwise noted. See
Figure 2 for a timing diagram.
Table 3.
Parameter 1
Limit at
TA = +25°C
Limit at TA = 0°C to +70°C
TA = −25°C to +85°C
Limit at
TA = −55°C to +125°C
Unit
Test Conditions/Comments
t1
t2
t3
t4
t5
t6
0
0
170
170
140
20
0
0
200
200
160
20
0
0
240
240
180
30
ns min
ns min
ns min
ns min
ns min
ns min
CS to WR setup time
CS to WR hold time
LDAC pulse width
Write pulse width
Data setup time
Data hold time
1
Temperature range as follows: J, K Versions: 0°C to +70°C
A, B Versions: −25°C to +85°C
S, T Versions: −55°C to +125°C
Rev. B | Page 4 of 16
AD7538
TIMING DIAGRAM
t1
t2
5V
CS
0V
t3
LDAC
5V
0V
t4
5V
WR
0V
t6
5V
DATA
0V
NOTES
1. ALL INPUT SIGNAL RISE AND FALL TIMES MEASURES FROM 10%
TO 90% OF 5V, tR = tF = 20ns.
VIH + VIL
2. TIMING MEASUREMENT REFERENCE LEVEL IS
.
2
3. IF LDAC IS ACTIVATED PRIOR TO THE RISING EDGE OF WR,
THEN IT MUST STAY LOW FOR t3 OR LONGER AFTER WR GOES HIGH.
Figure 2. Timing Diagram
Rev. B | Page 5 of 16
01139-002
t5
AD7538
ABSOLUTE MAXIMUM RATINGS
TA = +25°C unless, otherwise stated.
Table 4.
Parameter
VDD (Pin 23) to DGND
VSS (Pin 24) to AGND
VREF (Pin 1) to AGND
VRFB (Pin 2) to AGND
Digital Input Voltage (Pins 6 to 22)
to DGND
VPIN3 to DGND
AGND to DGND
Power Dissipation (Any Package)
To 75°C
Derates Above 75°C
Operating Temperature Range
Commercial (J, K Versions)
Industrial (A, B Versions)
Extended (S, T Versions)
Storage Temperature
Lead Temperature (Soldering, 10 sec)
Rating
−0.3 V, +17 V
−15 V, +0.3 V
±25 V
±25 V
−0.3 V, VDD +0.3 V
−0.3 V, VDD +0.3 V
−0.3 V, VDD +0.3 V
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
1000 mW
10 mW/°C
0°C to +70°C
−25°C to +85°C
−55°C to +125°C
−65°C to +150°C
300°C
Rev. B | Page 6 of 16
AD7538
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
VREF 1
24 VSS
RFB 2
23 VDD
IOUT 3
22 WR
DGND 5
(MSB) DB13 6
DB12 7
AD7538
21 CS
20 LDAC
TOP VIEW
(Not to Scale) 19 DB0 (LSB)
18 DB1
DB11 8
17 DB2
DB10 9
16 DB3
DB9 10
15 DB4
DB8 11
14 DB5
DB7 12
13 DB6
01139-003
AGND 4
Figure 3. Pin Configuration
Table 5. Pin Function Description
Pin No.
1
2
3
4
5
6 to 19
20
21
22
Mnemonic
VREF
RFB
IOUT
AGND
DGND
DB13 to DB0
LDAC
CS
WR
Description
Voltage Reference.
Feedback Resistor. Used to close the loop around an external op amp.
Current Output Terminal.
Analog Ground
Digital Ground.
Data Inputs. Bit DB13 (MSB) to Bit DB0 (LSB).
Chip Select Input. Active low.
Asynchronous Load DAC Input. Active low.
Write Input. Active low.
CS
LDAC
WR
Operation
0
1
0
Load input register.
1
0
X1
Load DAC register from input register.
0
0
0
Input and DAC registers are transparent.
1
1
X1
No operation.
X1
1
1
No operation.
+12 V to +15 V Supply Input.
Bias pin for high temperature low leakage configuration. To implement low leakage system, the pin should be
at a negative voltage. See Figure 6 and Figure 8 for recommended circuitry.
X
23
24
1
VDD
VSS
X = don’t care.
Rev. B | Page 7 of 16
AD7538
TERMINOLOGY
Relative Accuracy
Relative accuracy or endpoint nonlinearity is a measure of the
maximum deviation from a straight line passing through the
endpoints of the DAC transfer function. It is measured after
adjusting for zero error and full-scale error and is normally
expressed in least significant bits or as a percentage of fullscale reading.
Digital-To-Analog Glitch Impulse
The amount of charge injected from the digital inputs to the
analog output when the inputs change state is called digital-toanalog glitch impulse. This is normally specified as the area of
the glitch in either pA-secs or nV-secs depending upon whether
the glitch is measured as a current or voltage. It is measured
with VREF = AGND.
Differential Nonlinearity
Differential nonlinearity is the difference between the measured
change and the ideal 1 LSB change between any two adjacent
codes. A specified differential nonlinearity of ±1 LSB maximum
over the operating temperature range ensures monotonicity.
Output Capacitance
This is the capacitance from IOUT to AGND.
Gain Error
Gain error is a measure of the output error between an ideal
DAC and the actual device output. It is measured with all 1s
in the DAC after the offset error has been adjusted out and is
expressed in least significant bits. Gain error is adjustable to
zero with an external potentiometer.
Output Leakage Current
Output leakage current is current which appears at IOUT with the
DAC register loaded to all 0s.
Multiplying Feedthrough Error
This is the ac error due to capacitive feedthrough from the VREF
terminal to IOUT with the DAC register loaded to all zeros.
Rev. B | Page 8 of 16
AD7538
DAC SECTION
Switch A to Switch G steer equally weighted currents between
IOUT and AGND.
Figure 4 shows a simplified circuit diagram for the AD7538
DAC section. The three MSBs of the 14-bit data word are
decoded to drive the seven switches (A to G). The 11 LSBs
of the data word consist of an R-2R ladder operated in a
current steering configuration.
Because the input resistance at VREF is constant, it may be driven
by a voltage source or a current source of positive or negative
polarity.
The R-2R ladder current is ⅛ of the total reference input
current. ⅞ current flows in the parallel ladder structure.
2R
2R
2R
2R
2R
2R
R
2R
R
2R
2R
2R
2R
R/4
G
F
E
D
C
B
A
S10
S9
S0
RFB
IOUT
AGND
Figure 4. Simplified Circuit Diagram for the AD7538 DAC Section
Rev. B | Page 9 of 16
01139-004
R
VREF
AD7538
CIRCUIT INFORMATION
Figure 5 shows an equivalent circuit for the analog section
of the AD7538 DAC. The current source ILEAKAGE is composed
of surface and junction leakages. The RO resistor denotes the
equivalent output resistance of the DAC, which varies with
input code. COUT is the capacitance due to the current steering
switches and varies from about 90 pF to 180 pF (typical values)
depending upon the digital input. g(VREF, N) is the Thevenin
equivalent voltage generator due to the reference input voltage,
VREF, and the transfer function of the DAC ladder, N.
R/4
RO
VDD
R2
10Ω
1
23
2
VREF
VDD
RFB
LDAC
20
LDAC
CS
21
CS
C1
33pF
IOUT 3
AD7538
AGND 4
WR
22
WR
DB13 TO DB0 DGND
6
19
5
DIGITAL
GND
INPUT DATA
VSS
C2
4.7µF
+
24
R3
1kΩ
R4
47kΩ
RFB
IOUT
ILEAKAGE
A1
AD711
VO
ANALOG
GND
–15V
Figure 6. Unipolar Binary Operation
COUT
AGND
01139-005
g (VREF , N)
R1
20Ω
VIN
01139-006
EQUIVALENT CIRCUIT ANALYSIS
Table 6. Unipolar Binary Code Table
Figure 5. AD7538 Equivalent Analog Output Circuit
DIGITAL SECTION
The digital inputs are designed to be both TTL and 5 V CMOS
compatible. All logic inputs are static protected MOS gates with
typical input currents of less than 1 nA. To minimize power supply
currents, it is recommended that the digital input voltages be
driven as close as possible to 0 V and 5 V logic levels.
UNIPOLAR BINARY OPERATION (2-QUADRANT
MULTIPLICATION)
Figure 6 shows the circuit diagram for unipolar binary
operation. With an ac input, the circuit performs 2-quadrant
multiplication. The code table for Figure 6 is given in Table 6.
Capacitor C1 provides phase compensation and helps prevent
overshoot and ringing when high-speed op amps are used.
Binary Number In
DAC Register
MSB
LSB
11 1111 1111 1111
10 0000 0000 0000
00 0000 0000 0001
00 0000 0000 0000
Analog Output, VOUT
−VIN(16,383/16,384)
−VIN(8192/16,384) = −½VIN
−VIN(1/16,384)
0V
For zero offset adjustment, the DAC register is loaded with
all 0s and amplifier offset (VOS) adjusted so that VOUT is 0 V.
Adjusting VOUT to 0 V is not necessary in many applications,
but it is recommended that VOS be no greater than (25 × 10−6)
(VREF) to maintain specified DAC accuracy (see the Application
Hints section).
Full-scale trimming is accomplished by loading the DAC
register with all 1s and adjusting R1 so that VOUTA = −VIN
(16,383/16,384). For high temperature operation, resistors
and potentiometers should have a low temperature coefficient.
In many applications, because of the excellent gain TC and
gain error specifications of the AD7538, gain error trimming is
not necessary. In fixed reference applications, full scale can also
be adjusted by omitting R1 and R2 and trimming the reference
voltage magnitude.
Rev. B | Page 10 of 16
AD7538
BIPOLAR OPERATION (4-QUADRANT
MULTIPLICATION)
Table 7. Bipolar Code Table for the Offset Binary Circuit
of Figure 8
The recommended circuit diagram for bipolar operation is
shown in Figure 8. Offset binary coding is used. The code table
for Figure 8 is given in Table 7.
Binary Number In
DAC Register
MSB
LSB
11 1111 1111 1111
10 0000 0000 0001
10 0000 0000 0000
01 1111 1111 1111
00 0000 0000 0000
With the DAC loaded to 10 0000 0000 0000, adjust R1 for VO =
0 V. Alternatively, one can omit R1 and R2 and adjust the ratio
of R5 and R6 for VO = 0 V. Full-scale trimming can be accomplished by adjusting the amplitude of VIN or by varying the
value of R7.
The values given for R1, R2 are the minimum necessary to
calibrate the system for Resistors R5, R6, R7 ratio matched to
0.1%. System linearity error is independent of resistor ratio
matching and is affected by DAC linearity error only.
VDD = 15V
VREF = 10V
LEAKAGE CURRENT (nA)
60
When operating over a wide temperature range, it is important
that the resistors be of the same type so that their temperature
coefficients match.
LOW LEAKAGE CONFIGURATION
For CMOS multiplying DAC, as the device is operated at higher
temperatures, the output leakage current increases. For a 14-bit
resolution system, this can be a significant source of error. The
AD7538 features a leakage reduction configuration to keep the
leakage current low over an extended temperature range. One
may operate the device with or without this configuration. If VSS
(Pin 24) is tied to AGND then the DAC exhibits normal output
leakage currents at high temperatures. To use the low leakage
facility, VSS should be tied to a voltage of approximately −0.3 V
as in Figure 6 and Figure 8. A simple resistor divider (R3, R4)
produces approximately −300 mV from −15 V. The C2
capacitor in parallel with R3 is an integral part of the low
leakage configuration and must be 4.7 μF or greater. Figure 7
is a plot of leakage current vs. temperature for both conditions.
It clearly shows the improvement gained by using the low
leakage configuration.
Analog Output VOUT
+VIN(8191/8192)
+VIN(1/8192)
0V
−VIN(1/8192)
−VIN(8191/8192)
50
40
VSS = 0V
30
20
VSS = –0.3V
10
30
40
50
60
70
80
LDAC
R2
22Ω
1
23
2
VREF
VDD
RFB
R6
20kΩ
C1
33pF
R7
20kΩ
20 LDAC
CS
21 CS
WR
22 WR
A1
AGND 4
DB13 TO DB0 DGND
6
19
INPUT DATA
5
DIGITAL
GND
R5
10kΩ
IOUT 3
AD7538
VSS
AD711
R8
5kΩ, 10%
C2
4.7µF
+
24
R3
1kΩ
A2
AD711
VO
ANALOG
GND
R4
47kΩ
–15V
Figure 8. Bipolar Operation
Rev. B | Page 11 of 16
01139-007
VDD
100 110 120
Figure 7. Graph of Typical Leakage Current vs. Temperature for AD7538
VIN
R1
50Ω
90
TEMPERATURE (°C)
01139-008
0
AD7538
Substituting this expression into Equation 1 and assuming
zero gain error for the DAC (RIN = RFB), the transfer function
simplifies to
PROGRAMMABLE GAIN AMPLIFIER
The circuit shown in Figure 9 provides a programmable gain
amplifier (PGA). In it the DAC behaves as a programmable
resistance and thus allows the circuit gain to be digitally
controlled.
VOUT
2n
=−
VIN
N
DIGITAL
INPUT
The ratio N/2n is commonly represented by the term, D, and, as
such, is the fractional representation of the digital input word.
N
IOUT
VDD
A
VREF
VOUT
A VSS
NOTES
1. RESISTOR RFB IS ACTUALLY
INCLUDED ON THE DICE.
Figure 9. Programmable Gain Amplifier (PGA)
20 log 10
The transfer function of Figure 9 is:
Gain =
R EQ
VOUT
=−
VIN
R FB
(1)
REQ is the equivalent transfer impedance of the DAC from the
VREF pin to the IOUT pin and can be expressed as
R EQ =
(4)
Equation 4 indicates that the gain of the circuit can be varied
from 16,384 down to unity (actually 16,384/16,383) in 16,383
steps. The all 0s code is never applied. This avoids an open-loop
condition thereby saturating the amplifier. With the all 0s code
excluded there remains (2n – 1) possible input codes allowing a
choice of (2n – 1) output levels. In decibels the dynamic range is
VDD
01139-009
VIN
RFB
VOUT
− 2n − 1
=−
=
VIN
N
D
AD7538
GND
(3)
2 n R IN
(2)
N
where:
n is the resolution of the DAC.
N is the DAC input code in decimal.
RIN is the constant input impedance of the DAC (RIN = RLAD).
Rev. B | Page 12 of 16
VOUT
V IN
= 20 log 10 (2 n − 1) = 84 dB
AD7538
APPLICATION HINTS
OUTPUT OFFSET
CMOS DACs in circuits such as Figure 6 and Figure 8 exhibit
a code dependent output resistance, which in turn can cause a
code dependent error voltage at the output of the amplifier.
The maximum amplitude of this error, which adds to the DAC
nonlinearity, depends on VOS, where VOS is the amplifier input
offset voltage. To maintain specified accuracy with VREF at 10 V,
it is recommended that VOS be no greater than 0.25 mV, or (25 ×
10−6) (VREF), over the temperature range of operation. The AD711 is
a suitable op amp. The op amp has a wide bandwidth and high
slew rate and is recommended for ac and other applications
requiring fast settling.
In a multiple DAC system, the double buffering of the AD7538
allows the user to simultaneously update all DACs. In Figure 11,
a 14-bit word is loaded to the input registers of each of the DACs
in sequence. Then, with one instruction to the appropriate
address, CS4 (that is, LDAC) is brought low, updating all the
DACs simultaneously.
ADDRESS BUS
16-BIT
LATCH
ALE
CS1
CS4 CS3 CS2
8096
WR
CS
AD75381
LDAC
WR
AD0 TO AD15
GENERAL GROUND MANAGEMENT
ADDRESS
DECODE
DATA BUS
Because the AD7538 is specified for high accuracy, it is important to use a proper grounding technique. AC or transient
voltages between AGND and DGND can cause noise injection
into the analog output. The simplest method of ensuring that
voltages at AGND and DGND are equal is to tie AGND and
DGND together at the AD7538. In more complex systems
where the AGND and DGND intertie on the backplane, it is
recommended that two diodes be connected in inverse
parallel between the AD7538 AGND and DGND pins
(1N914 or equivalent).
DB0 TO DB13
CS
AD75381
LDAC
WR
DB0 TO DB13
CS
AD75381
MICROPROCESSOR INTERFACING
LDAC
The AD7538 is designed for easy interfacing to 16-bit microprocessors and can be treated as a memory mapped peripheral.
This reduces the amount of external logic needed for interfacing
to a minimal.
DB0 TO DB13
1LINEAR
CIRCUITRY OMITTED FOR CLARITY.
01139-011
WR
Figure 11. AD7538-to-8086 Interface: Multiple DAC System
AD7538-TO-8086 INTERFACE
AD7538-TO-MC68000 INTERFACE
Figure 10 shows the 8086 processor interface to a single device.
In this setup, the double buffering feature (using LDAC) of the
DAC is not used. The 14-bit word is written to the DAC in one
MOVE instruction and the analog output responds
immediately.
Figure 12 shows the MC68000 processor interface to a single
device. In this setup, the double buffering feature of the DAC
is not used and the appropriate data is written into the DAC in
one MOVE instruction.
ADDRESS BUS
A1 TO A23
16-BIT
LATCH
ADDRESS
DECODE
AD75381
AD13
AD0
1LINEAR
CIRCUITRY OMITTED FOR CLARITY.
AD75381
WR
R/W
DB0 TO DB13
DATA BUS
01139-010
AD0 TO AD15
D0 TO D15
DATA BUS
Figure 10. AD7538-to-8086 Interface Circuit
1LINEAR
CIRCUITRY OMITTED FOR CLARITY.
Figure 12. AD7538-to-MC68000 Interface
Rev. B | Page 13 of 16
CS
LDAC
DTACK
WR
WR
ADDRESS
DECODE
AS
LDAC
8096
ADDRESS BUS
MC68000
CS
DB0 TO DB13
01139-012
ALE
AD7538
A0 TO A15
The digital inputs to the AD7538 are directly connected to the
microprocessor bus in the preceding interface configurations.
These inputs are constantly changing even when the device is
not selected. The high frequency logic activity on the bus can
feed through the DAC package capacitance to show up as noise
on the analog output. To minimize this digital feedthrough
isolate the DAC from the noise source. Figure 13 shows an
interface circuit, which uses this technique. All data inputs are
latched from the bus by the CS signal. One may also use other
means, such as peripheral interface devices, to reduce the digital
feedthrough.
ADDRESS
DECODE
MICROPROCESSOR
SYSTEM
WR
D0 TO D15
1LINEAR
AD75381
CS
LDAC
EN
16-BIT
LATCH
WR
DB0 TO DB13
CIRCUITRY OMITTED FOR CLARITY.
Figure 13. AD7538 Interface Circuit Using Latches to Minimize Digital
Feedthrough
Rev. B | Page 14 of 16
01139-013
DIGITAL FEEDTHROUGH
AD7538
OUTLINE DIMENSIONS
1.280 (32.51)
1.250 (31.75)
1.230 (31.24)
24
13
1
12
0.280 (7.11)
0.250 (6.35)
0.240 (6.10)
0.325 (8.26)
0.310 (7.87)
0.300 (7.62)
0.100 (2.54)
BSC
0.060 (1.52)
MAX
0.210 (5.33)
MAX
0.195 (4.95)
0.130 (3.30)
0.115 (2.92)
0.015
(0.38)
MIN
0.150 (3.81)
0.130 (3.30)
0.115 (2.92)
0.015 (0.38)
GAUGE
PLANE
SEATING
PLANE
0.022 (0.56)
0.018 (0.46)
0.014 (0.36)
0.005 (0.13)
MIN
0.430 (10.92)
MAX
0.014 (0.36)
0.010 (0.25)
0.008 (0.20)
0.070 (1.78)
0.060 (1.52)
0.045 (1.14)
071006-A
COMPLIANT TO JEDEC STANDARDS MS-001
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
CORNER LEADS MAY BE CONFIGURED AS WHOLE OR HALF LEADS.
Figure 14. 24-Lead Plastic Dual In-Line Package [PDIP]
Narrow Body
(N-24-1)
Dimensions shown in inches and (millimeters)
0.098 (2.49)
MAX
24
13
1
12
PIN 1
0.200 (5.08)
MAX
0.200 (5.08)
0.125 (3.18)
0.023 (0.58)
0.014 (0.36)
0.310 (7.87)
0.220 (5.59)
1.280 (32.51) MAX
0.060 (1.52)
0.015 (0.38)
0.320 (8.13)
0.290 (7.37)
0.150 (3.81)
MIN
0.100
(2.54)
BSC
0.070 (1.78) SEATING
0.030 (0.76) PLANE
15°
0°
0.015 (0.38)
0.008 (0.20)
CONTROLLING DIMENSIONS ARE IN INCHES; MILLIMETER DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF INCH EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
Figure 15. 24-Lead Ceramic Dual In-Line Package [CERDIP]
(Q-24-1)
Dimensions shown in inches and (millimeters)
Rev. B | Page 15 of 16
100808-A
0.005 (0.13)
MIN
AD7538
15.60 (0.6142)
15.20 (0.5984)
13
24
7.60 (0.2992)
7.40 (0.2913)
12
2.65 (0.1043)
2.35 (0.0925)
0.30 (0.0118)
0.10 (0.0039)
COPLANARITY
0.10
10.65 (0.4193)
10.00 (0.3937)
1.27 (0.0500)
BSC
0.51 (0.0201)
0.31 (0.0122)
SEATING
PLANE
0.75 (0.0295)
0.25 (0.0098)
45°
8°
0°
1.27 (0.0500)
0.40 (0.0157)
0.33 (0.0130)
0.20 (0.0079)
COMPLIANT TO JEDEC STANDARDS MS-013-AD
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN.
060706-A
1
Figure 16. 24-Lead Standard Small Outline Package [SOIC_W]
Wide Body
(RW-24)
Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Model
AD7538JN
AD7538JNZ 1
AD7538KN
AD7538KNZ1
AD7538JR
AD7538JR-REEL
AD7538JRZ1
AD7538JRZ-REEL1
AD7538KR
AD7538KR-REEL
AD7538KRZ1
AD7538KRZ-REEL1
AD7538AQ
AD7538BQ
AD7538SQ
AD7538TQ
1
Temperature Range
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
−25°C to +85°C
−25°C to +85°C
−55°C to +125°C
−55°C to +125°C
Relative Accuracy
±2 LSB
±2 LSB
±1 LSB
±1 LSB
±2 LSB
±2 LSB
±2 LSB
±2 LSB
±1 LSB
±1 LSB
±1 LSB
±1 LSB
±2 LSB
±1 LSB
±2 LSB
±1 LSB
Full-Scale Error
±8 LSB
±8 LSB
±5 LSB
±5 LSB
±8 LSB
±8 LSB
±8 LSB
±8 LSB
±5 LSB
±5 LSB
±5 LSB
±5 LSB
±8 LSB
±5 LSB
±10 LSB
±6 LSB
Z = RoHS Compliant Part.
©2009 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D01139-0-1/09(B)
Rev. B | Page 16 of 16
Package Description
24-Lead PDIP
24-Lead PDIP
24-Lead PDIP
24-Lead PDIP
24-Lead SOIC_W
24-Lead SOIC_W
24-Lead SOIC_W
24-Lead SOIC_W
24-Lead SOIC_W
24-Lead SOIC_W
24-Lead SOIC_W
24-Lead SOIC_W
24-Lead CERDIP
24-Lead CERDIP
24-Lead CERDIP
24-Lead CERDIP
Package Option
N-24-1
N-24-1
N-24-1
N-24-1
RW-24
RW-24
RW-24
RW-24
RW-24
RW-24
RW-24
RW-24
Q-24-1
Q-24-1
Q-24-1
Q-24-1